Not applicable.
1. Field of the Invention
This invention relates to antenna elements and more particularly to an antenna element far use in an array antenna.
2. Background of the Invention
As is known in the art, there is an increasing trend to include radar systems in commercially available products. For example, it is desirable to include radar systems in automobiles, trucks boats, airplanes and other vehicles. Such radar systems must be compact and relatively low cost.
Furthermore, some applications have relatively difficult design parameters including restrictions on the physical size of the structure in addition to minimum operational performance requirements. Such competing design requirements (e.g. low cost, small size, high performance parameters) make the design of such radar systems relatively challenging. Among, the design challenges is a challenge to provide an antenna system which meets the design goals of being low cost, compact and high performance.
In automotive radar systems, for example, cost and size considerations are of considerable importance. Furthermore, in order to meet the performance requirements of automotive radar applications, (e.g. coverage area) an array antenna is required. Some antenna elements which have been proposed for use in antenna arrays manufactured for automotive radar applications include patch antenna elements, printed dipole antenna elements and cavity backed patch antenna elements. Each of these antenna elements have one or more drawbacks when used in an automotive radar application.
For example, patch antenna elements and cavity backed patch antenna elements each require a relatively large amount of substrate area and thickness. Array antennas for automotive applications, however, have only a limited amount of area for reasons of compactness and cost. Thus, antenna elements which can operate in a high density circuit are required. Printed dipole antennas can operate in a high density circuit environment, however, array antennas provided from printed dipole antenna elements give rise to xe2x80x9cblind spotsxe2x80x9d in the antenna radiation pattern.
It would, therefore, be desirable to provide an antenna element which is compact, which can operate in a high density circuit environment, which is relatively low cost and which can be used to provide an array antenna having relatively high performance characteristics.
In accordance with the present invention, an antenna element includes a cover layer disposed over a radiator layer having a first ground plane disposed thereon with the ground plane having an aperture therein. The radiator layer is disposed over a feed circuit layer which has a second ground plane disposed thereon. A cavity is provided in the radiator and feed circuit layers by disposing a plurality of via holes between the first and second ground plane layers. An antenna element feed couples energy between the feed circuit and the antenna element. A feed circuit couples energy between the antenna element feed and a butler matrix and is provided as an elevation feed which is interlaced between each of the antenna elements. With this particular arrangement, a compact slotted antenna element which utilizes a stripline-fed open ended dielectric filled cavity is provided. In one embodiment, the antenna element is provided from Low Temperature Co-fired Ceramic (LTCC) circuit substrates on which the multiple antenna elements can be disposed to provide a compact array antenna capable of switching between multiple antenna beams. The antenna element of the present invention requires only five layers and thus can be provided as a relatively low cost antenna. The radiator layers can be provided having capacitive windows formed therein for tuning the antenna element. By providing the feed circuit as an elevation feed which is interlaced between each of the antenna elements, a compact antenna which can operate in a densely packed environment is provided. A multiple beam array antenna was designed to radiate at 24 GHz. The entire antenna was fabricated in a single Low Temperature Co-fired Ceramic (LTCC) circuit. The design of the antenna included the radiating element (stripline-fed open-ended waveguide), .the beam farming network (Butler Matrix), radiator feed circuit, quadrature hybrid, power dividers, and interlayer transitions.
In accordance with a further aspect of the present invention, an array antenna comprises a plurality of slotted antenna elements, each of which utilizes a stripline-fed open ended dielectric filled cavity. With this particular arrangement, a compact array antenna which can provide multiple beams is provided. The antenna can be used in a sensor utilized in an automotive radar application. In a preferred embodiment, the sensor includes a transmit and a receive antenna. In a preferred embodiment, the transmit and receive antennas are provided as a bi-static antenna pair disposed an a single substrate. In other embodiments, however, a monostatic arrangement can be used.
In accordance with a still further aspect of the present invention, a switched beam antenna system includes a plurality of antenna elements, a butler matrix having a plurality of antenna ports and a plurality of switch ports with each of the antenna ports coupled to a respective one of the plurality of antenna elements and a switch circuit having an input port and a plurality of output ports each of the switch output ports coupled to a respective one of the plurality of switch ports of the butler matrix. With this particular arrangement, a multiple beam switched beam antenna system is provided. By providing the antenna elements from a single Low Temperature Co-fired Ceramic (LTCC) substrate, the antenna system can be provided as a compact antenna system. In a preferred embodiment the radiating element are provided from stripline-fed open-ended waveguide fabricated in the LTCC substrate and the Butler matrix, radiator feed circuit, quadrature hybrid, power dividers, and interlayer transitions are also provided in the LTCC substrate.